Visualise raster data with ggplot2

class: center, middle, inverse, title-slide

# Visualise raster data with ggplot2

---

layout: true
  
<div class="dk-footer">
<span>
<a href="https://rfortherestofus.com/" target="_blank">R for the Rest of Us
</a>
</span>
</div>

---

class: center, middle, dk-section-title
background-image:url("https://images.pexels.com/photos/23781/pexels-photo.jpg?auto=compress&cs=tinysrgb&dpr=2&h=750&w=1260")
background-size: cover

# Visualise raster data with ggplot2

---

# {ggplot2} and raster GIS

The `{ggplot2}` package on its own doesn't know how to visualise raster GIS datasets.

- The `{ggspatial}` package can visualise both `{raster}` and `{terra}` layers

- The `{stars}` package contains `geom_star()` that can be slotted into a "normal" `{ggplot2}` chart.

---

# {ggspatial}

We use the `layer_spatial()` function to add `{raster}` and `{terra}` layers to a `{ggplot2}` chart.

The "variable" used to fill the raster layer is called "band1" and is used in `aes()` as follows:

```r
ggplot() +
  layer_spatial(raster_data,
                aes(fill = stat(as.character(band1))))
```

---

# {stars}

We use `geom_stars()` like a normal geom.

The "variable" used inside aes() depends on the actual stars object itself.

```r
# stars object with 3 dimensions and 1 attribute
# attribute(s):
#              Min. 1st Qu. Median     Mean 3rd Qu. Max.
# L7_ETMS.tif     1      54     69 68.91242      86  255
# dimension(s):
#      from  to  offset delta                       refsys point values x/y
# x       1 349  288776  28.5 UTM Zone 25, Southern Hem... FALSE   NULL [x]
# y       1 352 9120761 -28.5 UTM Zone 25, Southern Hem... FALSE   NULL [y]
# band    1   6      NA    NA                           NA    NA   NUL
```